module PGJob
  class Job
    # Initialize with AR::connection or attributes for PG.connect
    def initialize(*args, &block)
      if args.first.respond_to?(:exec)
        @conn = args.first
        @can_finish = false
      else
        @conn = PG.connect(*args)
        @can_finish = true
      end

      if block_given?
        block.call(self)
        finish!
      end
    end

    # Creates jobs table
    def migrate!
      unless tables.include?('jobs')
        @conn.exec <<-SQL
          CREATE TABLE jobs (
            id SERIAL,
            name character varying(255),
            params text,
            status character varying(20),
            log text
          );
        SQL
      end
    end

    # Destroys jobs table
    def rollback!
      @conn.exec <<-SQL
        DROP TABLE IF EXISTS jobs;
      SQL
    end

    # Closes connection if possible
    def finish!
      if @can_finish
        @conn.finish
      end
    end

    # Creates new job
    def create(name, params = {})
      assert_symbol_keys!(params)

      sql = <<-SQL
        INSERT INTO jobs(name, params, status)
        VALUES('#{@conn.escape(name)}', '#{@conn.escape JSON.dump(params)}', 'wait')
        RETURNING id;
      SQL
      @conn.exec(sql).to_a.first['id'].to_i
    end

    # Returns name
    def name(id)
      sql = <<-SQL
        SELECT name
        FROM jobs
        WHERE id = #{id};
      SQL
      @conn.exec(sql).to_a.first['name']
    end

    # Sets/Returns status
    def status(id, value = nil)
      if value
        raise "wrong value" unless [:wait, :running, :success, :failed].include?(value.to_sym)
        sql = <<-SQL
          UPDATE jobs
          SET status = '#{@conn.escape value.to_s}'
          WHERE id = #{id};
        SQL
        @conn.exec(sql)
      else
        sql = <<-SQL
          SELECT status
          FROM jobs
          WHERE id = #{id};
        SQL
        @conn.exec(sql).to_a.first['status'].to_sym
      end
    end

    # Returns params
    def params(id)
      sql = <<-SQL
        SELECT params
        FROM jobs
        WHERE id = #{id};
      SQL
      symbolize_keys JSON.load(@conn.exec(sql).to_a.first['params'])
    end

    # Returns full log
    def log(id)
      sql = <<-SQL
        SELECT log
        FROM jobs
        WHERE id = #{id};
      SQL
      @conn.exec(sql).to_a.first['log']
    end

    # Adds log message
    def add_log(id, msg)
      sql = <<-SQL
        UPDATE jobs
        SET log = '#{@conn.escape [log(id), msg].compact.join("\n")}'
        WHERE id = #{id};
      SQL
      @conn.exec(sql)
    end

    private
    def assert_symbol_keys!(hash)
      hash.each do |key, value|
        unless key.is_a?(Symbol)
          raise "#{key} should be symbol"
        end

        if value.is_a?(Hash)
          assert_symbol_keys!(value)
        end
      end
    end

    def symbolize_keys(hash)
      out = {}
      hash.each do |key, value|
        if value.is_a?(Hash)
          out[key.to_sym] = symbolize_keys(value)
        else
          out[key.to_sym] = value
        end
      end
      out
    end
                           
    def tables
      sql = <<-SQL
        SELECT table_name
        FROM information_schema.tables
        WHERE table_schema = 'public';
      SQL

      @conn.exec(sql).map { |r| r['table_name'] }
    end
  end
end